Is it common?
prevalence is 0.8%
Differentiating features
This diagnosis is suspected based on signs and symptoms. It
is a "great mimicker" of other diseases and if there are
unexplainable signs and symptoms such as these, a TSH level should
be checked. A high TSH level and low serum T4 and free T4
are diagnostic.
Other features
Memory impairment, constipation, hoarseness, deafness, shortness
of breath, muscle and joint aches, tingling, chest pain, dry,
coarse, cold skin, eye swelling, thin hair, decreased reflexes,
hypertension, and slow heart rate
Cause
Hashimoto's thyroiditis and idiopathic myxedema
Iatrogenic: iodine 131 therapy for hyperthyroidism and subtotal
thyroidectomy
Drug-induced: Iodide deficiency or excess, lithium, amiodarone,
anti-thyroid drugs
Congenital: Synthetic enzyme defects and thyroid dysgenesis or
agenesis
Unnecessary studies
Serum T3 is of no value
Natural history untreated
If children are untreated, this results in cretinism (mental and motor
retardation, growth retardation and delayed puberty.
Untreated adults may be mild or severe. Mild would just
have the above symptoms for life. If severe, myxedema may
occur resulting in above symptoms being severe in nature with
additional findings of scaling of the skin, doughy feeling skin,
yellow-orange appearance to skin, variable degrees of heart
block, enlarged heart, and congestive heart failure, until a
fatal coma ensues.
Goals of therapy (Rx)
To bring free T4 (L-thyroxine) and TSH levels into normal range
and improve symptoms.
1st choice therapy
L-thyroxine
Other therapies used
Patients with myxedema with resulting adrenal insufficiency may
require glucocorticoids.
Treatments to avoid
This syndrome may be caused by amiodarone (Cordarone®, an
anti arrhythmic drug), lithium, and excessive
iodine.
Reason for Rx choices
Improve symptoms and prevent CNS problems.
References
Cecil's Essentials of Medicine, W.B.Saunders Company, 1993.
Other resources
Thyroid Disease
at Gland Central on the Web